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Patented Jan. 18, 1949 @O'F'FICE .-2 :Kenneth H;;Slagle,=.Mount Iiehanon;-. and;Robert S. -Bowman,rRittshurgh, BassaQSignOrs-MJOneS & Lang-hlinrSteel [Qrporation,,;l?ittsburgh,-.Ra.,

a. corporation of Pennsylvania .5 Claims. (Cl: 260-}290) I This-invention irelateszto-a process oi -separatingioneiiromz another; the pyridinebases comprisingztheafraction know-nrindustrially. as the if-betagamma-picoline; tiractionfl obtained from; the fractional distillationof coal tar, .or from coke overhgas.

2-';Annobjectaotioun invention is;- to..-provide a process sfor afraetionatingrthis -.grc up-,-v of, pyridine bases. Another object is v:tosprcw'ide a, process for; obtaining :the components ofthis group in a reasonably highlstate c t-purity; Another object is"v toiprovide -arcommercially:feasible process of obtainingftheseicomponentibases.

when. so called,-fbeta-,gammaepicoline traction comprises the-. threeipyridineabases boiling: in-the neighborhood-bf e44"? C; beta; or 3 -..picoline,-boiling ,at 444.0? C.,- 1 gamma Or';4:piGO1iH8,; boiling at;4441530 .and-2,6=lutidine; boiling at #14414? C, Alltthese components are. industrially-useful; but because oiethe mirtual coincidence of theiriboil ing-spoints rand .-the; ,eomplete amiscibility, of fall threemvitl'r water,alcohols, ketones, and hydrocarbon: .sol-vents; they {cannot beseparated by conventional-J ,distillatiom orl-.-.solvent extraction processes.-; A mumberzofi processes gfor thein 56 aration hasheen .devised,:but ,nonemas, been rsuccessful in fractionatingttheamixturez into its constituentncomponents ofireasonablyt-ihig h;purity at alreasonable-cost.

We have invented a.-=process .o-i .fract-ionating this mixture ro f picolines and. x-lutidine q-twhich yieldszthacomponentsinva high degree 56f purity. Our. invention is based-ton; the technique of fractional freezing, or crystallization.

The melting.pointstaofjithe:pure;pyridine bases are not .grouped, as closely as,. the boiling .points; e-picoline-meltsat +3:8C.,"2;fi=lntidine at 6.0 C. and B-picoline at -18.3 C."It'W0u1d appear that this rangetisiagreatrenouglr.toaffiord at least a partial. separation of the ..constituents by,fractionahireezing, but this is not,,inafact theecase. All threeconstituents exhibit the phenomenon of mndercooling to such amextent that when freezing ,finally starts the entire..mixture--.solidifies in an amorphous mass. We have discovered, however, that the benzoates of the picoline and lutidine bases exhibit undercooling characteristics such that they can be separated by fractional freezing. Our process, then, comprises the addition of benzoic acid to the beta-gamma-picoline fraction, controlled cooling to produce selective crystallization of at least two of the three benzoates in turn, each crystallization stage being followed by filtering or centrifuging to separate solid and liquid phases, and finally resolution of 3 eaehhenzoateinto the original pyridine base and benzoic= acid.

When benzoic acid is added to the picolinelutidine mixture and the solution slowly cooled,

. the i2,6=..utidine, benzoate first crystallizes, .tol-

lowedby the .4epicoline benzoate. It is notieasible to crystallize the 3-picoline benzoate from the. remaining..soluti0n,,as it undercools severely. Wefindv itmore. practical to purify this 3,-picoline benzoateqconcentrateiby regenerating the 3,-picoline ,with austrong galkali again. adding ,benzoic acid,..and ,again. freezing out .2,6 -lutidine and .lgpicoline .benzoates.

Wealso find thatlalthough it is possibletov carry outethe,separationv as, above. described. the process is more easily managed if the mixture of benzoates.i,s..diluted. witha solvent, preferably a. hydrocarbon solvent such as toluene. The addition oisuch a solvent reduces the viscosity of the.1iq.- uidatlow temperatures ..and facilitates the steps 0I. .f1ltering .oncentrifuging. the solid from therliquidlphases.

The, process or our, invention willunow be described in .detail; .To,.the mixture of :pyridine bases is, added a substantially. .molecular equivalentoffbenzoic acid. Suiiicient toluene or other hydrocarbon solventis'added to reduce the viscosity of the mixture to .a..low.-value.r The .mixture is,.coole.d withoutstirring to a temperature inthejrange -7P to -.10 CL, preferably the-lower figure, At this temperatureneedle crystals ofthe 2,'6 lutidine'benzoate begin to form and separate from theliquid. .Themixture is held at this temperaturejfor atime sufficient to allow the bulkof the lutidine compound to .freeze, and the solids and liquid are separated by any convenient means, such as vacuum filtration orcentrifuging. vIn thiststage about. of .th'e..2,6-,lutidine is obtained as abenzoate of substantially purity; ","IIhe?'2,6- lutid ine is recovered by dissolving the lutidine. benzoate,' in water, adding slightly .more sodium'hydroxid'e, or other strong base, than is equivalent tothehenzoic acid, and distilling ofi the 2,'6'-lutidine-water azeotrope. Dry2,6-.lutidine. is .ohtai-ned refluxing the, ,lutidine-water solution withbenzene, separating the water, and fractionally distilling the resulting benzene-Intidine mixture. The 2,6-lutidine so recovered is substantially 100% pure.

The liquid mixture remaining after filtration of the 2,6-lutidine benzoate crystals is slowly cooled to a temperature of about -20 C. During this cooling a 2,6-lutidine-4-picoline intermediate crystallizes and is separated from the liquid. As this intermediate is small in amount, totalling These crystals, of plate form, are separated from,

the liquid, again by vacuum filtration'or centrifuging, and the dry 4-picoline of about 95% purity is recovered by exactly the same methods" as are used for the 2,6-lutidine.

The separation of the crystals of -picoline benzoate leaves a filtrate whichis abouta 70% concentration of 3-picoline benzoate, Aspreviously mentioned, this concentrate may be further treated by first regenerating with a strong alkali, such as sodium hydroxideto obtain the pyridine bases, which are separated from-the sodium benzoate by steam distillation. Benzoic acid is added to the mixture of pyridine bases and the mixture of benzoates is then subjected a second time to the fractional crystallization process as herein described, which results in some further yield of 2,6-lutidine and 4-pico'line. The concentration of the 3-picoline mixture cannot be raised above about 80%, however, as the other two components appear to be soluble in 3-picoline to some extent even at low temperatures.

The benzoic acid used in our process need not be lost, but may be regenerated from the solution of caustic compound, in every case, by acidifying the solution with a mineral acid, such as sulfuric acid. The sulfuric acid displaces the weaker benzoic acid from the compound, and the benzoic acid, having a low solubility in water, separates from the water and sulfate, and may be obtained by filtering or centrifuging.

The yield of the process of our invention is reasonably high. For example, to a ten gallon batch of the beta-gamma-picoline fraction weighing 80 pounds may be added 103 pounds of benzoic acid and 1.3 gallons of toluene. From this may be obtained 1'? pounds of 2,6-lutidine and 30 pounds of 4-picoline, each of a purity above 95%, and 28.5 pounds of about 80% 3- picoline concentrate. In addition about 98 pounds of the benzoic acid may be recovered at a cost of 45 pounds of sulfuric acid and about 36 pounds of sodium hydroxide.

The invention is not limited to the preferred embodiment but may be otherwise embodied or practiced within the scope of the following claims.

We claim: I

l. The method of separating a mixture of the pyridine bases 3-picoline', l -picoline and 2,6- lutidine, which comprises adding benzoic acid and toluene to the mixture, cooling slowly to a temperature in the range -7 to 10 0., whereby the 2,6-lutidine benzoate is caused to crystallize, separating these crystals from the liquid, cooling this liquid to a, temperature of about -20 whereby the 4-picoline benzoate is caused to crystallize, separating these crystals from the liquid, and regenerating the pyridine bases from their respective benzoates. q

2. The method of separating a, mixture of the pyridine bases a-picoline, 4-picoline and 2,6- lutidine, which comprises adding benzoic acid and toluene to the mixture, cooling slowly to a temperature in the range -7 to -10 C., whereby the 2,6-lutidine benzoate is caused to crystallize, separating these crystals from thej liquid: cooling this liquid to a temperature of about 0., whereby the 4-pico1ine benzoate is caused to crystallize, separating these crystals from the "pyridine bases 3-picoline, 4-picoline and 2,6-

liquid, adding strong alkali to the liquid to regenerate a mixture of pyridine bases, separating the mixture of pyridine bases, adding benzoic acid, subjecting the solution containing the mixture ofb'en'zoates to selective crystallization, selectively separating the solid benzoates from the solution,- and regenerating the pyridine bases from their respective benzoates.

3. In a method of separating mixture of the lutidine, the steps which comprise adding benzoic acid to the mixture, cooling to a'temperature below the freezing point of 2,6-lutidine benzoate but above thefreezing points of 4-picoline benzoate and 3-picoline benzoate, separating the re: sulting crystals from the liquid, cooling the-liquid to a temperature below the freezing poi'ntof- 4'-- picoline benzoate but above the freezing pointof 3-picoline benzoate, and separating the resulting crystals from the liquid.

4. In a method of separating a mixture of the pyridine bases 3-picoline, 4-picol-ine and 2,6- lutidine, the steps which comprise adding benzoic acid and a solvent to the mixture, cooling to a temperature below the freezing point of 2,6'-lutidine benzoate but above the freezing points of 4-picoline benzoate and B-picoline benzoate,- separating the resulting crystals from the liquid, cooling the liquid to a temperature below the freezing point of 4-picoline benzoate but above the freezing point of 3-picoline benzoate and separatingthe resulting crystals from the liquid; 5. In the method of separating"2,6-lutidine from a mixture of pyridine bases containing the same and at least one of the other pyridine bases 3-picoline and 4-picoline, the steps which comprise adding benzoic acid to the mixture, cooling to a temperature below the freezing point of 2,6- lutidine benzoate but above the freezing points of the other pyridine base benzoates,'separating the resulting crystals from the liquid, and regenerating 2,6-1utidine from said crystals.

- KENNETH SLAGLE. ROBERT S. BOWMAN;

Name Date 2,402,158 "G10Wakl June 18, 1946 2,432,063 Cislak Dec/2, 194.7; 2,432,064 Cislak Dec. :2, 1947 2,432,065 

